The Unsaturated-Fat Oxidases With Reference to Their Coupled Reactions in Cereal Flours

Hawthorn, John (1954) The Unsaturated-Fat Oxidases With Reference to Their Coupled Reactions in Cereal Flours. PhD thesis, University of Glasgow.

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Abstract

The practice of adding chemical oxidising agents to the wheat flours used in breadmaking is of long standing. Recent work has shown that certain hazards to public health arise from these additions, but the introduction of legislation to prevent their use has been delayed by technical difficulties in finding an acceptable alternative. The function of these additions is to bleach the carotenoid pigments in the flour and to modify the wheat proteins in such a way as to render the flour more suitable for making bread of a fine quality. Any breadmaking process which dispenses with chemical treatment without sacrifice to quality is therefore of considerable importance. Details of such a process have been published, but the chemical mechanism of its action has been a matter of conjecture. In the belief that the process involved the intervention of that group of enzymes known as the unsaturated-fat oxidases, a study of these systems was undertaken. The best characterised member of the group is lipoxidase, an enzyme which is abundantly present in soya-beans. The development of a suitable system for the study of coupled carotene bleaching by lipoxidase gave rise to difficulties associated with the heterogeneous nature of the reactions involved, but these were eventually circumvented. In the system adopted, the oxidase under investigation was allowed to react in a buffer solution which had been equilibriated with atmospheric oxygen, and which contained a small concentration of pure sodium linoleate as substrate. Arrangements were made to disperse carotene in the solution at the beginning of the reaction, the course of which was followed by observing the degree of bleaching in a suitable instrument. The unsaturated-fat oxidases may be divided into two classes, namely, the true lipoxidases which are believed to be without a metallic prosthetic group, and the haem proteins, which under appropriate circumstances are able to catalyse the oxidation of fats in a rather similar fashion to the lipoxidases. The enzymes soya lipoxidase and ox-liver catalase were selected as typical representatives of each class, and their behaviour was studied in the carotene-linoleate system with respect to such variables as reaction time, enzyme concentration, substrate concentration, and pH. The inherent pH optimum of soya lipoxidase received detailed attention because of its importance in distinguishing between true lipoxidase systems and haem catalysis. The optimum pH of this enzyme has been the subject of considerable controversy among workers in this field. Aided by these studies, attention was given to the behaviour of unsaturated-fat oxidase in flour during the course of its preparation for baking. Coupled with a rapid method of analysis for carotenoid pigments in bread and flour, a test-baking system was used to follow the course of the reactions during the mixing of bread doughs. It was established from these studies that the bleaching of bread by the process under consideration was catalysed by the unsaturated-fat oxidases, and that the "improvement" or modification of the wheat proteins was brought about by the increased access of oxygen which is a feature of the process. Arising out of these investigations an improved method of carrying out this process was suggested and has been tested successfully on a commercial scale.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Medical ethics
Date of Award: 1954
Depositing User: Enlighten Team
Unique ID: glathesis:1954-79085
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 11:44
Last Modified: 05 Mar 2020 11:44
URI: http://theses.gla.ac.uk/id/eprint/79085

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